1. Field of the Invention
The present invention relates to a signal transmission system for high definition television that can restore a second television signal which is superior in quality to a first television signal such as an NTSC (National Television System Committee) television signal: the transmitting end of the system transmits a first television signal including a video signal, audio signals, etc., through a main transmission line, as well as a third television signal including a high definition components obtained as the difference between the second and the first television signal through an auxiliary transmission line; the receiving end of the system receives and synthesizes the first television signal transmitted through the main transmission line and the third television signal transmitted through the auxiliary transmission line to produce the second television signal.
As the first television signal transmitted through the main transmission line, there are a video signal and an audio signal according to the NTSC standard television system. On the other hand, there is a preferable television signal compatible with NTSC signal. Although this television signal is similar to the standard television signal in the bandwidth of a transmission line, and in the transmission signal format, the television signal can be transmitted as a high definition television signal by using various band compression techniques.
2. Description of the Prior Art
A television system so-called an ATV system (Advanced Television System) has been proposed mainly by USFCC. This is a series of transmission systems of high definition televisions compatible with the conventional NTSC system. Various types of systems are researched and proposed at the present time. In the video signal in one of those ATV systems, a high frequency component of a stationary picture are multiplexed with a low frequency component by the three dimensional signal processing or the like: the component higher than 4 MHz in a luminance signal of the stationary picture is multiplexed into four interframe intervals in the form of subsampled data or the like; and then, a vertical high-band component of the luminance signal and the high-band component of chrominance signal (higher than 1.5 MHz for I signal, and higher than 0.5 MHz for Q signal) are superposed onto upper and lower masking portions formed by the upper and lower masking method, and are transmitted.
With respect to the processing of the video signal of this example, pending U.S. patent application Ser. No. 07/498,778, entitled "Receiver And Channel Compatible Encoding/Decoding System for High Definition Video" was filed on Mar. 26, 1990 by the same inventors of the present invention. As to the processing of the audio signal, another U.S. patent application Ser. No. 07/499,874 entitled "Method and System for Transmitting and Receiving PCM Audio Signals in Combination With A Video Signal" was filed on Mar. 27, 1990 by the same inventors of the present invention (now U.S. Pat. No. 5,072,297, issued Dec. 10, 1991). Details of respective matters are given therein. In the video signal of the above example, a vertical high-band component and a horizontal high-band component of the luminance signal higher than the television signal of the NTSC system, and high-band component of the chrominance signal are extracted from a wide-band input television signal (a second television signal); the extracted components are multiplexed into the low-band component of the wideband television signal corresponding to the NTSC television signal with maintaining the bandwidth thereof, and then transmitted.
On the other hand, with regard to the audio signals of the above example, at least the same contents of the audio signals transmitted by FM modulation in the NTSC system are pulse-code-modulated (PCM), are multiplexed into the blanking interval of the video signal after the bit compression, and are transmitted together with the FM modulated audio signals. When the code error rate is small on the transmission line, demodulated PCM (pulse-code-modulated) audio signals are produced as audio signals. Accordingly, using the video signal and the audio signal transmission systems proposed by the above-mentioned U.S. patent applications makes it possible to transmit the video signal and the audio signals having much higher definition compared with those of the NTSC television system within the same transmission bandwidth as that of the NTSC system. The video and audio signals multiplexed and bit compressed by the above processing in the transmission systems, however, are inferior in grade to the original signals.